Loughner, the suspected gunman in the assassination attempt on Rep. Gabrielle Giffords and mass shooting outside a Tucson, Ariz., supermarket, posted a series of incoherent YouTube manifestos that rambled about “conscious dreaming,” sleepwalking, grammar, terror and revolution.

In the most disturbing rant published under his name, Loughner posted a video depicting a man dressed as the Grim Reaper setting fire to the American Flag.

Playing in the background is “Bodies” by the metal band Drowning Pool with its chilling intro, “Let the bodies hit the floor.”

His Myspace page, which was deleted yesterday, included a enigmatic sign-off: “Goodbye friends . . . Please don’t be mad at me.”

Loughner attempted to enlist in the Army but was rejected, a law-enforcement source told The Post.

“Jared Loughner is a United States Military recruit at MEPS [military entrance processing station] in Phoenix,” he wrote in another post accompanied by eerie music. “I didn’t write a belief on my Army application and the recruiter wrote on the application: None.”

Pima County Sheriff Clarence Dupnik said Loughner had a “criminal background” and had previously made death threats, but it was not clear against whom, except that the threats were not towards Giffords.

The Arizona Daily Star said he was arrested in Oct. 2007 for possession of drug paraphernalia and was again arrested on an unknown charge a year later.

In another paranoid rant, the suspect wrote: “Reading the second United States Constitution, I can’t trust the current government because of the ratifications; The government is implying mind control and brainwash on the people by controlling the grammar.”

Among his favorite books listed on his Myspace profile, Loughner included “Mein Kampf,” “The Communist Manifesto” and “The Wizard of Oz.”

Loughner, 22, a Tucson resident and student at Pima Community College, is an only child who still lives with his family, neighbors said.

“When he was a young boy, he was very nice but kind of a loner,” said longtime neighbor Lynn Riach, who remembered often hearing him practicing the saxophone.

“We’re a really tight-knit neighborhood. We know all our neighbors and the Loughner family kept to themselves,” Riach said. “The parents loved their son very much.”

Other neighbors said they recall Loughner only rarely emerging from his house, usually to walk his dog. He always wore headphones, they said.

He made a drastic change to his shaggy appearance last summer when he shaved his head, a neighbor said.

“My favorite interest was reading, and I studied grammar,” he wrote on a Myspace profile that was deleted yesterday afternoon.

Loughner dropped out of high school after his junior year in 2006 but later attended community college.

A former classmate at Pima said he was “obviously very disturbed.”

Lynda Sorenson, who took a math class with Loughner, told the Arizona Daily Star, that he would constantly disrupt the class “with nonsensical outbursts.”

And Lydian Ali said the alleged gunman would laugh maniacally to himself in their poetry class.

“It almost seemed like he was on his own planet, because his comments would have nothing to do with what we were talking about,” she told the paper.

Excerpts from Jared Lee Loughner’s YouTube postings

“The majority of citizens in the United State of America have never read the United States of America’s Constitution. You don’t have to accept the federalist laws. Nonetheless, read the United State of America’s Constitution to apprehend all of the current treasonous laws. You’re “

“The current government officials are in power for their currency, but I’m informing you for your new currency! If you’re treasurer of a new money system, then you’re responsible for the distributing of the new currency. “

“No! I won’t trust in God.”

“In conclusion, reading the second United States Constitution, I can’t trust the current government because of the ramifications: The government is implying mind control and brainwash on the people by controlling grammar. No! I won’t pay debt a currency that’s not backed by gold and silver!”

“My hope – is for you to be literate! If you’re literate in English grammar, then you comprehend English grammar. The majority of people, who reside in District 8, are illiterate – hilarious.”

“I know who’s listening: Government officials, and the People. Nearly all the people, who don’t know this accurate information of a new currency, aren’t aware of mind control and brainwash methods.”

“If I define terrorist then a terrorist is a person who employs terror or terrorism, especially as a political weapon. If you call me a terrorist then the argument to call me a terrorist is Ad hominem. You call me a terrorist. Thus, the argument to call me a terrorist is Ad hominem.”